It is common to provide a hydraulic apparatus, such as a hydraulic pump, hydraulic motor, or integrated hydraulic transmission (i.e., a hydraulic pump and hydraulic motor in the same assembly), with a bypass valve. The bypass valve is actuatable between a normal mode condition and a bypass mode condition. In the normal mode condition, the bypass valve prevents a free flow of fluid between the pressure conduits and a central conduit of the hydraulic apparatus. In the bypass mode condition, the bypass valve enables the free flow of fluid between the pressure conduits and the central conduit of the hydraulic apparatus.
Bypass valves are common when the hydraulic apparatus forms part of a vehicle propulsion system. For example, when the hydraulic apparatus is a hydraulic pump of a hydrostatic transmission for a turf machine, actuating the bypass valve to the bypass mode condition enables towing of the turf machine, i.e., movement of the turf machine under a power other than its own, as the flow of fluid resulting from the movement of the wheels of the turf machine flows freely (or with little resistance) between the conduits of the pump. When the bypass valve is in the normal mode condition, towing of the turf machine is extremely difficult. Any movement of the vehicle results from fluid flowing through small gaps formed in the hydraulic apparatus as a result of manufacturing tolerances, such as, e.g., very small gaps located between the pistons and the bores in a piston pump.
One known hydraulic apparatus is a hydraulic pump having an end block with a central conduit interposed between first and second pressure conduits. A first valve is located between the central conduit and the first pressure conduit and may be opened, for example, in response to pressure spikes, to fluidly connect the central conduit and the first pressure conduit. Similarly, a second valve is located between the central conduit and the second pressure conduit and may be opened, for example, in response to pressure spikes, to fluidly connect the central conduit and the second pressure conduit. A bypass valve is located in the central conduit and includes a lobed portion that is interposed between the first and second valves. The bypass valve is rotated by ninety degrees between its normal mode condition, in which the lobed portion is spaced away from the first and second valves, and a bypass mode condition, in which the lobed portion of the bypass valve engages and opens the first and second valves.